Chapter 2: Molecular Structure and Bonding

The valence shell electron pair repulsion model provides a predictive framework for determining molecular geometries by minimizing electrostatic repulsion between electron pairs, with applications to simple molecules like boron trifluoride and phosphorus pentachloride, while accounting for effects of lone pairs on bond angles and stereochemically inert lone pairs in heavier main-group elements. Valence bond theory conceptualizes bonding as the overlap of atomic orbitals, introducing sigma and pi bonds and the critical concept of hybridization, where atomic orbitals blend to form new hybrid orbitals including sp, sp², sp³, sp³d, and sp³d² configurations that explain tetrahedral, trigonal-planar, and more complex geometries, with emphasis on promotion and the bonding in hypervalent compounds. Molecular orbital theory treats bonding electrons as delocalized across the entire molecular framework, developed through construction of molecular orbital diagrams for homonuclear diatomics including nitrogen, oxygen, and fluorine to explain bond order, magnetic properties, and ionization patterns, then extended to heteronuclear molecules like hydrogen fluoride and carbon monoxide where orbital mixing and frontier orbital concepts like HOMO and LUMO characterize reactivity. Polyatomic systems are analyzed using symmetry-adapted linear combinations and Walsh diagrams for predicting geometry changes with bonding electrons, with attention to delocalized bonding in electron-deficient species. The chapter connects molecular structure to quantifiable properties including bond length, bond dissociation enthalpy, and electronegativity scales, integrating Pauling values with electronegativity differences to classify bonding character using frameworks like the van Arkel-Ketelaar triangle. Finally, systematic rules for assigning oxidation states are presented as essential tools for describing electron distribution and predicting chemical behavior across diverse inorganic compounds.